Jon Hamm as Don Draper in the first episode of the sixth series of Mad Men: 'A lot has changed," says creator Matthew Weiner. Photograph: Michael Yarish/AP

It is nearly a year since Mad Men fans were left wondering whether Don Draper would stay faithful to his new wife or return to a hedonistic path towards his likely self-destruction.

On Wednesday they will have their answer – albeit very possibly an opaque one – as the feted US drama about advertising executives in 1960s New York returns to Sky Atlantic for its sixth series.

Such is its creator Matthew Weiner's determination to keep the new season under wraps, in an age when the internet "spoiler" has become common, that previewers have even been asked not to reveal the time in which the new season is set.

Series five ended in the spring of 1967 with Draper, played by Jon Hamm, drinking alone in a smoky bar, propositioned by a mystery woman who asks him: "Are you alone?"

Weiner, not entirely averse to talking about the new series, has said: "The whole story of the season is the answer to 'Are you alone?'" He described the first two episodes as a "movie unto themselves … A lot has changed."

What can be said with certainty is that this will be its penultimate season, Weiner having indicated that it will come to an end – after 26 more episodes – next year.

The new season opener is called The Doorway – fans avoiding any sort of spoiler should look away now – and was said by one US previewer to include a wedding, two deaths and a "dramatic physical transformation" by one of its leading characters.

Despite having joined a rival ad agency in the last series, Peggy Olson, played by Elisabeth Moss, will return. Weiner said the makers had a "ton of conversations" about how much she would figure in the new series.

Mad Men's influence – and the amount of attention it receives in the press – far outweighs its audience. The last series had an opening night audience of 98,000, a fraction of the 9 million people who tune into BBC1's Sunday night hit drama, Call the Midwife.

Ratings fell since it was bought by Sky last year (its previous season premiere, on BBC4, was watched by 355,000 viewers). But for Sky the benefit of the show is not in overnight audience figures but driving satellite subscriber numbers.

"It was classy, cool, and pressed all the buttons for the London metropolitan media elite that meant it was always going to punch above its weight in terms of publicity," said Ben Preston, editor of the Radio Times.

"This series sounds as though Don has got his wanderlust back, which always made it compulsive viewing. It is not as fresh as it was, but it is still excellent television."

Winner of 15 Emmy awards and four Golden Globes since it began on US cable network AMC in 2007, Mad Men has also been credited with changing the face of high-street fashion. Banana Republic even has a Mad Men collection, catering for both men and women.

"It has had an enormous effect on the way men dress, much more than any other TV show," said Alex Bilmes, editor of Esquire. "If you think of a high-street store like Top Man, suits are incredibly sharp, well cut, with skinny lapels and very thin ties. They look like the sort of thing a young man would have worn in 1962."

Bilmes added: "It's a great irony of Mad Men that the show is an extremely effective satire on the vacuousness of consumerism – despite all of the money and the girls and the car, Don Draper isn't happy – and yet the show itself has been used as this fantastic marketing tool."

Fashionistas fearing that the new series will prompt a headlong rush towards flappy lapels and kipper ties can rest easy. Although the show has moved on from the spring of 1967, it has not moved on far, with Draper's fondness for a sharp suit apparently undimmed.

"It looks like they are playing it quite safe," said Robert Johnston, associate editor of GQ. "It appears the women's outfits have been allowed to change more than the men's."

He added: "Young men today want to wear suits, but they don't want to wear the suits their fathers wore, so bizarrely they have gone back to the suits their grandparents wore. It's skipped a generation."

Mad Men will return in the US on Sunday, three days before the UK. Weiner said viewers should ideally watch the last 10 minutes of season five – which played out to the theme tune of that year's James Bond, You Only Live Twice. Given Draper's dual identity, it was entirely appropriate.